/*
 * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.tools.javac.processing;

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;

/**
 * Utility class to determine if a service can be found on the path that might
 * be used to create a class loader.
 * 
 * <p>
 * <b>This is NOT part of any supported API. If you write code that depends on
 * this, you do so at your own risk. This code and its internal interfaces are
 * subject to change or deletion without notice.</b>
 * 
 */
// based on sun.misc.Service
class ServiceProxy {
	static class ServiceConfigurationError extends Error {
		static final long serialVersionUID = 7732091036771098303L;

		ServiceConfigurationError(String msg) {
			super(msg);
		}
	}

	private static final String prefix = "META-INF/services/";

	@SuppressWarnings("rawtypes")
	private static void fail(Class service, String msg)
			throws ServiceConfigurationError {
		throw new ServiceConfigurationError(service.getName() + ": " + msg);
	}

	@SuppressWarnings("rawtypes")
	private static void fail(Class service, URL u, int line, String msg)
			throws ServiceConfigurationError {
		fail(service, u + ":" + line + ": " + msg);
	}

	/**
	 * Parse the content of the given URL as a provider-configuration file.
	 * 
	 * @param service
	 *            The service class for which providers are being sought; used
	 *            to construct error detail strings
	 * 
	 * @param url
	 *            The URL naming the configuration file to be parsed
	 * 
	 * @return true if the name of a service is found
	 * 
	 * @throws ServiceConfigurationError
	 *             If an I/O error occurs while reading from the given URL, or
	 *             if a configuration-file format error is detected
	 */
	@SuppressWarnings("rawtypes")
	private static boolean parse(Class service, URL u)
			throws ServiceConfigurationError {
		InputStream in = null;
		BufferedReader r = null;
		try {
			in = u.openStream();
			r = new BufferedReader(new InputStreamReader(in, "utf-8"));
			int lc = 1;
			String ln;
			while ((ln = r.readLine()) != null) {
				int ci = ln.indexOf('#');
				if (ci >= 0)
					ln = ln.substring(0, ci);
				ln = ln.trim();
				int n = ln.length();
				if (n != 0) {
					if ((ln.indexOf(' ') >= 0) || (ln.indexOf('\t') >= 0))
						fail(service, u, lc,
								"Illegal configuration-file syntax");
					int cp = ln.codePointAt(0);
					if (!Character.isJavaIdentifierStart(cp))
						fail(service, u, lc, "Illegal provider-class name: "
								+ ln);
					for (int i = Character.charCount(cp); i < n; i += Character
							.charCount(cp)) {
						cp = ln.codePointAt(i);
						if (!Character.isJavaIdentifierPart(cp) && (cp != '.'))
							fail(service, u, lc,
									"Illegal provider-class name: " + ln);
					}
					return true;
				}
			}
		} catch (FileNotFoundException x) {
			return false;
		} catch (IOException x) {
			fail(service, ": " + x);
		} finally {
			try {
				if (r != null)
					r.close();
			} catch (IOException y) {
				fail(service, ": " + y);
			}
			try {
				if (in != null)
					in.close();
			} catch (IOException y) {
				fail(service, ": " + y);
			}
		}
		return false;
	}

	/**
	 * Return true if a description for at least one service is found in the
	 * service configuration files in the given URLs.
	 */
	public static boolean hasService(Class<?> service, URL[] urls)
			throws ServiceConfigurationError {
		for (URL url : urls) {
			try {
				String fullName = prefix + service.getName();
				URL u = new URL(url, fullName);
				boolean found = parse(service, u);
				if (found)
					return true;
			} catch (MalformedURLException e) {
				// should not happen; ignore it if it does
			}
		}
		return false;
	}
}
